In addition to immersing the material in water and hoping for the best results, there are many things to do in strand pelletizing. Here are some suggestions for excluding some guesses. #processingtips #bestpractices

Shown here is a typical water bath system. However, the process of making a good pellet is much more complicated than putting a rope in water and hoping for the best.

What goes into the Gaylord box usually depends on the dynamics between the extruder and the pelletizer.

Shown here is the internal mechanical working principle of a typical strand pelletizer. The photo shows an open view of the cutting room.

Strand pelletization is a mature technology. Except for some improvements in metallurgy and design to ensure safety and customer convenience, the process is almost the same as 50 years ago. One of my mentors once described this process as "a wring-dry washing machine with a lawn mower." Although the assessment is correct to a certain extent, it is not a convenient fact and can be used as an excuse not to make improvements in the production workshop.

In view of its function, the design of the strand pelletizer is very simple. A pair of feed rollers pull the wire harness from the extrusion die, and then transfer them to the spiral rotating knife, which is cut against a fixed anvil (called a bedknife). The process is the same whether the operation is to process one wire at a speed of 10 pounds per hour or to process 200 wires at a speed of 20,000 pounds per hour. Perhaps it is this simplicity that conceals the true nature of the extrusion line.

The relationship between the kinetic granulator and the extrusion line between the extruder and the granulator The long-term challenge facing the relationship between the granulator and the extrusion line is, "If you provide me with good wire, I will provide you with good pellets." The granulator is not Magic machines; they will not turn bad strands or strands that have not been properly adjusted or transported into good pellets. In fact, it doesn't matter whether the rotor is sharp or blunt, whether the roller is new or worn, or whether the bearing is good or bad... It is foreseeable that bad steel strands will produce bad particles. These machines will make them at an astonishing speed.

Historically, many sciences have been applied to extruders and upstream conveying components. Just read a magazine like this to learn about various products in barrel and screw technology (single-screw and twin-screw) and temperature control to understand all the engineering dedicated to these systems.

Likewise, the pelletizer and downstream components have also been carefully designed to operate reliably under very adverse conditions, and in many cases. Structural materials and surface enhancement materials extend the service life of the equipment and redefine the duration of continuous movement to a large extent. Careful attention has been paid to safety, ease of use and maintainability to improve the operator’s experience with the machine.

Although these two dynamics (extruder/upstream and pelletizer/downstream) have received considerable attention and engineering focus, what happens between the equipment and the two systems seems to be largely ignored. From the extrusion die to the feed table of the pelletizer, in the eyes of casual observers, the common perception is "dip it in some water and see what happens."

How to remedy unqualified granular resin manufacturers and composite manufacturers to invest heavily to develop products and bring them to the market. However, whether the science is correct, the thermal and physical properties, strength and performance, and color are perfect, it does not matter to the customer. If the customer opens the box and sees sticks, granules, zippers, or particles that look like shredded cocktail sticks-to him or her, the box is substandard. Wet or variable bulk density particles, which are bridged in the feed throat, or contaminated by fines degraded in the barrel, have little chance to prove their value as a final product.

Obviously, half of the problems related to unqualified particles are the distance between the mold and the cutting machine and how the strands transform from the molten phase to the solid. If the strands are not properly adjusted, the pelletizer can easily become a waste maker.

When setting up the extrusion line, the operator usually has a setting table to define the barrel temperature, etc., but when adjusting the strands used for cutting, he/she is often alone. In many cases, various strange floor brooms, PVC pipes and insufficient air knives have exacerbated this situation.

Although the focus here is on the process, it is important to have the right tools for any job. In today's market, many trading tools have been redesigned to increase the efficiency of their basic purpose. Just imagine: a vacuum stretch dryer that actually works. So, where should we go?

In most cases, getting started involves recognizing that the "old look" may have some room for improvement. The following assumes that the upstream melting stage requirements have been properly met. The operator must start with the prescribed method and list the various process elements of each material.

These values ​​are usually realized through guided empiricism based on reliable theories, known facts, and a little bit of trial and error. Once established, these should become the basis for the production line setup table-and it is important to use it for every shift. Otherwise...Imagine a car maintenance staff, each member can act on their own.

Determine downstream value Determine and monitor indicators based on product formulations to reduce waste and eliminate the guesswork of setting up an extrusion line. The goal here is to allow the operator to make fewer decisions to explain, instead relying on empirical data that produces predictable results.

For equipment downstream of the mold, these indicators should include: • Granulator variables, including rotor composition, number of teeth, rotor gap, feed roller composition, feed roller gap, and cylinder pressure. • The feed and speed of the pelletizer running nominally at a given extruder speed. • Process water temperature during operation. • Residence time (distance) in the water bath. • The positioning of the guide rollers in the water bath. • The target pellet temperature after cutting.

Particles are "witnesses", can see everything in the process, and can be tempted to reveal 95% of upstream failure modes. Riddles are how to read signs and react to what is observed. Science is repeatable, and if you pay attention to establishing reliable baselines—in other words, writing them down—it will be much easier to find the root cause of quality problems. For example, if the rotor and bedknife are known to be sharp and set at the proper gap, the presence of fine particles indicates that there is a strand adjustment problem.

After evaluating the particles, it is equally important to know what corrective actions to take, which can sometimes be completely counterintuitive. But following some simple guidelines during the setup process will double the chances of front-end success and greatly reduce the need to hunt down witches when things get worse.

There are often mixing production lines, where the output of the extruder has almost doubled, and the pelletizer has accelerated to meet the demand, but within the same processing range, the number of strands remains the same. This scene is full of trouble and will only cause problems for the operator.

There are many equipment to choose from, and in many cases, the installation of the equipment is seen as the last step of improvement. In fact, the choice of equipment is just the beginning, and its successful deployment relies on consistent and researched methods. There are some important factors in the process downstream of the extruder that control the result of entering the Gaylord box. 

A mixer that recognizes these factors and makes the necessary investment in time and resources to control these factors will only produce better pellets than a mixer that does not recognize these factors.

About the author: John Bell

John Bell is the regional sales manager of Reduction Engineering Scheer in Kent, Ohio, a supplier of pelletizers and shredders with other branches in Germany, Brazil, and China. He is a veteran with 25 years of experience in the plastics industry and has held various functions including product and inventory control manager, manufacturing manager, and operations manager. Contact: (814) 657-1017; jbell@reductionengineering.com; reduction engineering.com.

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